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Full text of "Text Book Of Mechanical Engineering"

I2O6

Appendix  VI.

Iff

I '(' ?

c

falls also to the position in the diagram : while the pump K re-fills,
and the action is repeated.

To keep the air vessel supplied with air, a snifting valve R1 is
fitted between suction and delivery; and the'valves p and Q serve
to empty the chamber L of air and water respectively, when it is
desired to stop the action of the apparatus. • •

With this pump 60 cubic feet of power water per minute at a
fall of 3 feet has been made to lift 300 cubic feet of clear water to
a height of 360 feet in 24 hours; which corresponds to an
efficiency of 41 per cent.; but a maximum of 70 per cent, efficiency
may be looked for in the case of all impulse rams under
favourable circumstances.

P, 730. Air Vessels for Pumps.—The air in air vessels
becomes gradually absorbed during the working of the pump,
especially at higher pressures. It is for this reason that air vessels
are not permissible in accumulator pumps (see p. 734). Tore-
charge such a vessel with air, two cocks may be used, one at the
top and one at the bottom of the vessel, so that water may be

drawn off below and air re-admitted above. If it be desired to
admit it automatically while at work, a snifting valve, a separate air
pump, or an c air injector' as it is termed, may be adopted. The
first of these, shewn in Fig. 1061, is placed between the suction
and delivery valves; and consists of a gun-metal chamber F,
containing a ball A which rolls backward and forward on account
of the pump stroke. When rolled leftward, air is drawn inward
at E, while the escape of water on return stroke is prevented by
a rightward roll; and the whole may be put out of action or
adjusted by the screwed plug D.

The air injector in Fig. 1062 is a much better contrivance.    A